PINKHAM NOTCH, N.H (CBS) – Twelve hikers survived an avalanche while trying to climb to the peak of Mt. Washington in New Hampshire.

Three of the hikers were swept away some 800 feet.

Group members tell WBZ-TV that Andy Politz has a broken leg, while Keith Zeier has injuries to his shoulder and hip. J.P. Politz has been treated and released.

Thom Pollard, who was on the trek, said he saw it coming. “I yelled ‘avalanche’,” said Pollard. “A slab broke off about 35 feet wide, maybe 8 inches deep and that’s what went down and picked up Andy, Keith and JP and they were swept all the way down to the bottom of the gully.”

“Everybody was hit by the avalanche, all four rope teams of three were hit by it,” said Pollard.

Stephanie White was also on the trek.

Andy Politz and his son J.P. on the trail Thursday before the avalanche.

“All I heard was ‘avalanche’,” recounted White. “Next thing I know a wall of snow just hits me.”

The three who were swept away somehow made it out of the ravine after about two hours, and they were met by Snow Rangers and volunteer rescuers. The nine others endured a grueling trek back down the mountain that took almost 6 hours.

The avalanche struck about eight hours into the climb.

The avalanche conditions posted Thursday were ‘moderate’, meaning a natural avalanche was unlikely but a human-triggered one was possible.